Fundamentals: Understanding Flat Networks

Jeremy Littlejohn02/02/12

Understanding Flat Networks

The traditional tiered network design is a staple of today's LAN and data center networks. However, this design has limitations caused in part by Spanning Tree Protocol (STP), which restricts the number of paths that traffic can take through the network. That restriction can affect performance and reliability requirements that are emerging because of virtualization and other factors, such as the convergence of storage and data networks.

An alternative network design, called a flat network or a fabric, is now available to IT. A flat network opens more paths and can increase available bandwidth. Flat network options include both standards-based approaches, such as TRILL (Transparent Interconnection of Lots of Links) and SPB (Shortest Path Bridging), as well as proprietary vendor approaches. All these approaches address shortcomings of STP and can make a data center network more flexible and responsive to the changing demands of highly virtualized environments.

However, a flat network also has its downsides, including the need to rearchitect the LAN. Depending on the approach that IT takes to a flat network, it may also require new gear; for instance, TRILL will likely require hardware upgrades because it uses a new frame type that has to be added to the standard Ethernet frame. Meanwhile, the proprietary approaches will lock IT to a single vendor.

This report examines the limitations of tiered networks and STP, explains the alternatives that allow IT to build a flat network, outlines potential downsides of this new approach, and offers guidance to help IT determine whether a flat network is a fit. (S4070212)